The present invention relates to an electromagnetic wave absorption material and a manufacturing method thereof, especially to an electromagnetic wave absorption material having bamboo charcoal as dieletric loss material and a manufacturing method thereof.
In an industrial society, electrical appliances are essential to our daily lives. Household appliances such as fans, hair dryers, juicers, and microwave ovens all generate electromagnetic wave that is harmful to human health. For example, household alternative current frequency is 60 Hertz (Hz). AC power reverses direction 60 times per second. Thus direction of the magnetic filed changes 60 cycles per second. By making the magnetic field direction change, a current is induced to flow and this lead to damages of human bodies. As to mobile phones that virtually everyone has one also generates strong electromagnetic wave. For example, dial the mobile phone in front of computer screens or radio receivers, the computer screen flicker like crazy while the radio has a buzzing noise. Moreover, the microwave oven also generates strong electromagnetic wave. Thus absorption or shielding of electromagnetic wave has become an important issue.
Refer to Taiwanese patent No. 469283, a manufacturing method of dielectric electromagnetic wave absorption material is disclosed. Liquid polyurethane (PU) resin is added with conductive carbon black, carbon powder, conductive fiber, and microballoons and the mixture is stirred into syrupy and then is molded into microwave absorbing material. Refer to Taiwanese patent No. 567643, a modified Salisbury Screen having a conductive ground plane, a (low dielectric constant composite material formed by two kind of materials, and a reflective surface is disclosed. Refer to Taiwanese patent No. 566077, an electromagnetic wave absorption material consisting of 5-50 wt % multi-layer carbon nanocapsules and resin is disclosed. As to Taiwanese publication application No. 200605772, a crosslinked electromagnetic wave absorption material made by extrusion molding is disclosed. Refer to U.S. Pat. No. 6,465,098B2, an electromagnetic wave absorbing material made by shaping a resin composition containing 5 to 10 parts by weight of a carbon black and 1 to 10 parts by weight of a gas phase growth carbon fiber in a resin based on 100 parts by weight of the resin is provided.
However, the slurry of the dielectric electromagnetic wave absorption material in Taiwanese patent No. 469283 has high viscosity. Firstly, a special-designed 3000-6000 rpm high speed mill is used to mix part of carbon black with the resin and then carbon powder, conductive fiber, and microballoons are added so that the slurry becomes more and more sticky. Next a 300-600 rpm low-speed high viscosity mixer mixes the mixture evenly and then the mixture is coated on a test piece. The manufacturing processes and equipments are quite complicated and the used conductive fillers are environmental-unfriendly chemical compounds. The modified Salisbury Screen disclosed in Taiwanese patent No. 567643 is double-layer so that the manufacturing processes are more complicated than single-layer material. In U.S. Pat. No. 6,465,098B2, although the use of gas phase growth carbon fiber to replace conventional carbon fiber reduces amount of carbon black and carbon fiber being added, the conductive fillers are still not environmental friendly. In Taiwanese patent No. 566077, the multi-layer carbon nanocapsules added in resin also don't meet environmental concerns.
Bamboo charcoal is powder similar to carbon black or graphite and is made from bamboo sintered at high temperature. Due to features of deodorization, bacteria resistance, moisture absorbance and infra-redemitting, bamboo charcoal is broadly applied to daily accessories such as food, cloth and fabric. In the present invention, bamboo charcoal is used to replace chemical compounds such as conductive carbon black, carbon powder, conductive fiber and graphite for satisfying environmental requirements.